Arc extinguishing structure for an electric circuit interrupter



March 21, 1961 Filed June 29, 1959 T. H. LEE ARC EXTINGUISHING STRUCTUREFOR AN ELECTRIC CIRCUIT INTERRUPTER 2 Sheets-Sheet 1 Inventor: Thomas H.Lee,

b His Attorney.

March 21, 1961 T. H. LEE 2,976,382

ARC EXTINGUISHING STRUCTURE FOR AN ELECTRIC CIRCUIT INTERRUPTER 2Sheets-Sheet 2 Filed June 29. 1959 Inventor: Thomas H. Lee

by His Attohneg United States Patent ARC EXTINGUISHING STRUCTURE FOR ANELECTRIC CIRCUIT INTERRUPTER Thomas H. Lee, Media, Pa., assignor toGeneral Electric Company, a corporation of New York Filed June 29, 1959,Ser. No. 823,731

18 Claims. (Cl. 200 144) This invention relates to arc-extinguishingstructure for an electric circuit interrupter and, more particularly, toarc-extinguishing structure which is especially, though not exclusively,suited for use in circuit interrupters of the vacuum type.

The usual vacuum-type circuit interrupter comprises a vacuum chamber inwhich a circuit-interrupting arc is established across an arcing gapbetween two electrodes. Assuming that the circuit is an alternatingcurrent circuit, the arc maintains itself until about the time a naturalcurrent zero is reached, after which the arc is prevented fromreigniting by the high dielectric strength of the vacuum.

One way of increasing the interrupting capacity of such an interrupteris by moving the terminals of the are at high speed along suitablearc-running surfaces provided within the interrupter. Such movementtends to minimize the amount of metallic vapors generated from thearc-running surfaces by the arc and tends also to increase the degree ofdiffusion of the vapors that are generated. These factors enable thevacuum to recover its dielectric strength at an increased rate after acurrent zero and thus render the vacuum more capable of preventingre-establishment of the arc during this critical interval.

In a vacuum circuit interrupter, it is highly desirable that arc motionbe rotational rather than translational. This follows from the fact thatvacuum arcs tend to move at very high speeds (considerably higher thanthe speeds occurring under corresponding conditions in more dense media,such as liquids and gases), and unless the path of arc motion isrecurrent, as is the case with rotational movement, there will beinsufiicient arc-ruin ning surface length available to accommodatecontinuous arc-motion. Since continuous arc-motion contributes toincreased interrupting capacity, the desirability of rota tionalarc-motion in obtaining increased interrupting capacity will beapparent.

Another way in which the interrupting capacity of a vacuum interruptercan be increased is by dividing the circuit-interrupting arc into aplurality of shorter arcs, or arclets, across a plurality ofseries-related gaps. After a current zero has been reached, the totaldielectric strength which is developed across the series-related gapsexceeds that which would be developed across a single gap had the arcbeen allowed to persist across the single gap. The result is increasedvoltage-interrupting ability and increased current-interrupting abilityas well.

An object or" my invention is to provide a simple arcextinguishingstructure which employs both of these principles, i.e., rapid arc-motionin a recurrent path and division of an are into series-related smallerarcs, to aid in extinguishing the arc.

Another object of my invention is to effect the desired arc-rotation bymagnetic means which is structurally simple and which requires noexternal coils or other similar and cumbersome magnetic devices forsuccessful rotation of the short series-related arcs.

2,975,382 Patented Mar. 21, 196i Another object is to construct thearc-extinguishing structure in such a manner that operation of themagnetic arc-rotating means for any one of the arcing gaps does notinterfere with operation of the arc-rotating means for the remainingarcing gap or gaps.

In my arc-extinguishing structure the short arcs or arclets that areformed across the secondary gaps are biased radially outwardly by aradially-outwardly-acting magnetic loop effect. Another object is torotate the arclets about such a path that this radially-outwardlyactingmagnetic loop efiect does not significantly retard or oppose therotational motion of the arclets during any portion of their rotationaltravel.

In carrying out my invention in one form, I provide within a vacuumchamber a pair of electrodes defining therebetween a main arcing gapacross which a circuitinterrupting arc is adapted to be established.Surrounding this main arcing gap, I provide a plurality of pairs ofannular disc-shaped members radially spaced from the electrodes. Thedisc-shaped members of each pair are spaced apart to define between thetwo disc-shaped members a secondary arcing gap of annular shapesurrounding the main gap. Means are provided for driving thecircuit-interrupting are from the main arcing gap radially outwardlyinto contact with the disc-shaped members so as to divide the are into aplurality of seriesrelated arclets respectively bridging the secondaryarcing gaps. Thereafter the arclets are driven onto the outer peripheralregion of the disc-shaped members by means providing a magnetic forceacting to hold said arclets on said outer peripheral region forsubstantially all angular positions of said arclets. These arclets aredriven repetitively about the outer peripheral region of the disc-shapedmembers by magnetic forces derived as a result of slot means extendingfrom the outer periphery of at least one disc-shaped member of each pairin such a manner that the current path extending through this onedisc-shaped member to an arclet terminal located at substantially anyangular point on the outer peripheral region has a net componentextending generally tangentially with respect to the periphery in thevicinity of the arclet terminal.

For a better understanding of my invention, reference may be had to thefollowing description taken in con junction with the accompanyingdrawing, wherein:

Fig. 1 is a sectional view of a vacuum-type circuit in terrupterembodying one form of my invention.

Fig. 2 is a sectional view taken along the line 2-2 of Fig. 1.

Fig. 3 is a view similar to that of Fig. 2 but showing a modification ofthe structure shown in Fig. 1.

Fig. 4 is a sectional view taken along the line 4-4 of Fig. 1.

Referring now to the interrupter of Fig. 1, there is shown a highlyevacuated envelope 10 comprising a cylindrical casing 11 and a pair ofmetallic end caps 12 and 13 closing off the ends of the casing. Thecasing 11 is of an imperforate vacuum-tight construction and is joinedto the end caps by means of suitable seals 14 forming a vacuum-tightconnection between the end caps and the casing 11.

The casing 11 is constructed from a series of collinearly arrangedcylinders 16, 17, 18, 19, 20, and 21 of an insulating material such asglass and a series of annular metallic structures interconnecting theinsulating cylinders. The annular metallic structure interconnecting theinsulating cylinders 16 and 17 comprises a pair of rings 22 or L-shapedcross-section with an annular disc 24 welded between the radiallyextending flanges of the L-shaped rings 22 in such a manner as toprovide a vacuum-tight seal between the rings 22. The opposite ends ofthe L-shaped rings 22 are embedded in the adjacent insulating cylindersto provide a known type of vacuum-tight seal between the rings 22 andthe insulating cylinders.

The annular metallic structures interconnecting the other ably thickerthan the annular disc 24. The reason for this will appear more clearlyhereinafter.

Located within the envelope is a pair of separable cup-shaped contacts,or electrodes, and 31 shown in their engaged or closed-circuitpositions. The upper contact 30 is a stationary contact suitably securedto a conductive rod 30a which at its upper end is united to the upperend cap 12, which serves as one electrical terminal of the interrupter.The lower contact 31 is a movable contact joined to a conductiveoperating rod 31a which is suitably mounted for vertical movement. Theoperating rod 31a projects through an opening in the lower end cap 13and a flexible bellows 34 provides a seal about the rod 31a to allow forvertical movement of the rod 31a without impairing the vacuum inside theenvelope 10. As shown in Fig. 1, the bellows 34 is secured in sealingrelationship at its respective opposite ends to the operating rod 31aand the end cap 13. The lower end cap 13 serves as the other terminal ofthe interrupter and is electrically connected to the conductiveoperating rod 31a by suitable means, such as conductive braid 33, whichrelieves the bellows 34 of any current-carrying duty.

Coupled to the lower end of the operating rod 31a, suitable actuatingmeans (not shown) is provided which is capable of driving the contact 31out of engagement with the contact 30 and into the dotted line positionof Fig. 1 so as to open the interrupter and which is also capable ofreturning the contact 31 to its illustrated solidline position so as toclose the interrupter. A contactopening operation will soon be explainedin greater detail.

Each contact is of a cup-shape form and has a central recess 35surrounded by an annular contact making area 36. These annularcontact-making areas 36 abut against each other when the contacts are intheir closed position of Fig. l and are of such a diameter that thecurrent flowing through the closed contacts follows a loop-shaped pathL, as is indicated by the dot-dash lines of Fig. 1. This loop-shapedpath has a magnetic effect which tends in a well-known manner tolengthen the loop. As a result, when the contacts are separated to forman are between the areas 36, the magnetic efiect of the loop will impelthe arc radially outward.

For receiving the respective terminals of the are when it is impelledradially outward by the magnetic loop effeet, a pair of annulararc-runners 37 and 38 of a gen erally conical form are provided. Theupper arc-runner 37 is mechanically and electrically joined to the uppercontact 30, whereas the lower arc-runner 38 is mechanically separatefrom the movable contact 31 but electrically connected thereto by meansof a tubular support 38a, slightly flared at its upper end, fastened tothe lower end cap 13 and located at the inner periphery of the arcrunner38. Any current flowing through either of these arc-runners to an arcterminal located thereon must flow from the inner periphery of thatparticular runner radially outward. Thus the path for such current willcoact with the arc to form a radially-outwardly bowing loop circuit.Accordingly, when the arc terminals are located at any point on therunners 37 and 38, the radially-outwardly acting-loop circuit is stillpresent to impel the arc radially outward. For example, note theradiallyoutwardly bowing loop circuit when the arc is passing through atypical position on the arc-runners such as shown at 39; The fact thatthe lower arc-runner 38 is separate from the movable contact 31appreciably reduces the mass of the structure that the interrupteractuating means is required to accelerate during an interrupter op- 4eration and therefore contributes to the desired high operating speeds.

When an arc is initiated by contact-separation, the upper arc terminalis first driven off the contact making area 36 of contact 30 onto theupper arc-runner 37, and shortly thereafter, as the lower contact 31approaches its dotted line open position, the lower arc terminal isdriven onto the lower arc-runner 38. Because the lower arc-runner 38surrounds the movable contact, the lower arc terminal will be drivenonto the lower arc-runner irrespective cf its particular circumferentiallocation at this instant. The magnetic loop ettect drives the arcterminals radially outward at high speed along the arc runners until thearc encounters arc-splitting and rotating means 40 surrounding theannular arc-runners 37 and 38. The arc-splitting and rotating means 40acts in a manner soon to be described to divide the arc into a pluralityof series-related shorter arcs, or arclets, and thereafter to rotatethese arclets about the longitudinal axis of the interrupter.

The arc-splitting and rotating means 40 comprises a plurality of discs41, 42, 43, 44, 45, and 46 arranged in substantially parallelspaced-apart planes to define a series of secondary arcing gaps betweencertain of the discs, as will soon be pointed out more clearly. Theupper disc 41 is supported on the upper end cap 12 by means of aconductive tube 48 integrally united at one end to the disc 41 at theinner periphery of the disc 41 and integrally united at its other endwith the upper end cap 12. Lower disc 46 is similarly joined to thelower end cap 13 by means of a conductive tube 49 integrally joined atits opposite ends to the disc 46 and the end cap 13. The upper set ofintermediate discs 42 and 43 are conductively interconnected by means ofa conductive tube 50 integrally joined at its longitudinally-oppositeends to the discs 42 and 43 at the inner peripheries of the discs 42 and43. Likewise, the lower set of intermediate discs 44 and 45 areconductively interconnected by means of a conductive tube 2 integrallyjoined at its opposite ends to the discs 44 and 45 at the innerperipheries of the discs. The location of the tubular conductors 49-52at the inner periphery of the discs contributes in an important mannerto the desired performance of my arc-extinguishing structure, as willsoon become more apparent.

The upper intermediate structure 42, 43, St is supported from the casing11 by means of the previously described annular support 26, which iswelded or otherwise secured at its inner periphery to the tube 50. Thelower intermediate structure 44, 45, 50 is likewise sup ported from thecasing 11 by means of the supporting annulus 23 which is welded orotherwise secured at its inner periphery to the tube 52.

As will be apparent from Fig. 1, the insulating cylinders 16 and 17electrically isolate the discs 41 and 42 from each other, and thus afirst secondary arcing gap 53 is defined between these two discs 41 and42. The insulating cylinders 18 and 19 isolate the discs 43 and 44 fromeach other and thus a second secondary arcing gap 54 is defined betweenthese two discs 43 and 44. Similarly, the insulating cylinders 20 and 21electrically isolate discs 45 and 46 from each other so that a thirdsecondary arcing gap 55 is defined between the discs.45 and 46.

Each of the discs 41-46 is provided with slots 57, shown in Fig. 2,extending from the outer periphery of the disc inward. These slotscollectively divide each of the discs into a series of discrete segments58 angularly spaced about the inner periphery of each disc. In thepreferred form of my invention illustrated in Fig. 2, these slots 57 areshown as being of a generally spiral configuration terminating in amouth 59 at the disc periphery. Each slot extends from its mouth 59 in agenerally tangential direction with respect to the periphery andterminates only after extending at least to a point near the angularposition of the mouth of an adjacent slot. Preferably, the adjacentslots angularly overlap each other as is shown in Fig. 2. The importanceof the above-described slot configuration will soon be pointed out inmore detail.

Assume now that an arc established during a circuit interruptingoperation is driven radially outward along the arc-runners 37 and 38. Assoon as the arc encounters the arc-splitting means 40, it is dividedinto three shorter series-connected arcs across the respective arcinggaps 53, 54, and 55. Each of these shorter arcs, or arclets, continuesto move radially-outward until its two terminals reach the outerperipheral region of the discs. A typical position for the upperterminal of the arc across the upper gap 53 is shown for example in Fig.2 where the arc terminal is designated 60. Considering now that currentis flowing to or from the upper arc terminal 60 solely through the tube48 at the inner periphery of the disc 41, it will be apparent thatbecause of the slots 57 substantially all of the current flowing betweenthe conductive tube 48 and the arc terminal 60 is concentrated in thatparticular segment 58 which is then carrying the arc terminal. Becauseof the generally spiral configuration of the slots 57, this current isrequired to follow a path which is to an effective extent tangentialwith respect to the disc periphery in the region of the are, as isillustrated by the dotted line of Fig. 2. As a result of this tangentialconfiguration of the current path, the magnetic loop has developed a nettangential force component. This not tangential force component drivesthe arc in an angular, or circumferential, direction about the discperiphery, causing it to move to the end of the segment 58 and to jumpacross the slot 57 to the next segment 58. The current flow to the arcis then concentrated in this next segment, and because of theconfiguration of this segment, there is a new tangentially-acting loopwhich continues motion of the arc around the contact periphery. For eachof the segments 58, there is a net tangential force component on the areacting in the same angular direction, and, as a result, circumferentialmotion of the arc continues at high speed until the arc is finallyextinguished. It will be apparent, of course, that if the arc is notextinguished before one revolution is completed, motion will continuerepetitively about the disc periphery until the arc is finallyextinguished.

It will thus be. seen that my arc-splitting and rotating structure 40acts not only to divide the main are into a plurality of series-relatedshorter arcs but also to rotate the shorter arcs' about the longitudinalaxis of the interrupter. Such are motion tends to minimize the amount ofvapors generated from the are running surfaces by the arc and tends alsoto increase the degree of diffusion of the vapors that are generated.These factors enable the vacuum to recover its dielectric strength at anincreased rateafterra current zero and, thus, render the vacuum morecapable of p eventing reestablishment of the arc during this criticalinterval. Dividing the main arc into three series-related arcs alsocontributes to increased current and voltage interrupting capacitybecause the total dielectric strength developed across theseries-related arcing gaps after a current zero exceeds that which wouldhave been developed across a single gap had the arc been allowed topersist across the single gap.

' It is to be noted that when the arclets have been established acrossthe secondary arcing gaps 53, 54, 55, the

current paths leading to the arclets no longer extend.

through the arc-runners 37 and 38 but rather extend through theconductive tubes 48 and 49. This follows from the fact that these tubes48 and 49 are directly connected to the discs 41 and 46, respectively,rather than being electrically isolated therefirom, as is the case witharc-runners 37 and 38, which are separated from the discs 41 and 46 bymeans of vacuum gaps 70 surrounding the outer peripheries of thearc-runners. These gaps prevent current from flowing through the tubes48 and 49 While the arc is still on the runners 37 and 38 and thusinsure 6 that the magnetic loop circuit acts in a' radially-outwarddirection during such interval.

In the disclosed interrupter, the net tangential force component actingon each series-related arclet is more pronounced when the arclet islocated near the outer periphery of the disc, as compared to when thearc is located near the inner periphery of the disc. It is thereforeimportant that the arclets be consistently driven on to the outerperipheral region of the discs, rather than be allowed to hang on to theinner peripheries, where there is no appreciable arc-rotating force. Toassure that the arclets are driven onto the outer periphery, I locateand construct the conductors leading to and from the discs- 41-46 insuch a manner that the current path leading to and from the arc terminalon the disc always forms with the are a loop that has a magnetic .eflectacting radially outward. In this regard, it is to be noted that thetubular conductors 48-52 leading to and from the discs 41-46 are locatedat the inner peripheries of the discs. Hence, any current flowingthrough a disc to or from the terminal of an arclet must follow a paththat extends radially outward from the inner periphery of the disc, thusproviding a radially-outwardly acting loop circuit with the arc, as isdesired. To provide for the transient situation that occurs when theterminal of an arclet is positioned at the inner periphery of the discs,each disc is provided with a bevel b at its inner periphery. Because ofthis bevel the radially innermost position on the disc at which anarclet is likely to be positioned is at the radially outer periphery ofthe bevel, as is illustrated for example by the position of arclet 62 isFig. 1. Even at this position, the current path 63 extending through thetubes 48 and 50 through the terminals of the arclet forms a loop bowingradially outward and therefore providing a magnetic force actingradially outward on the arclet. As the arclet moves radially outwardfrom this point, the loop and, hence, the radially-outwardly actingmagnetic force becomes more pronounced, thus tending to bias the arclettoward the outer periphery of the disc where the arc-rotating force isgreatest.

It will be apparent that the tubular conductor 50 between the adjacentdiscs 42 and 43 in forcing all the current flowing between these discsto follow a path through the inner periphery of the discs 42 and 43,assures that a radially-outwardly-acting loop circuit will be present onthe arclet 62a at gap 54 no matter where the arclet at the upper gap 53is located. Accordingly, the arclet at the gap 54 can be driven on tothe outer periphery of discs 43 and 44 and rotated in the desired mannerirrespective of the location of the arclet at gap 53. Similarly, thearclet at gap 53 can be driven onto the outer disc periphery and rotatedin the desired manner irrespective of the location of the arclet at gap54. A similar independence is present between the arclet 62b at thelower gap 55 and the other arclets due primarily to the inner peripherallocation of the various tubular conductors 48-52. Thus, it will beapparent that the operation of the magnetic means at any one of the gapsdoes not interfere with the operation of the magnetic means at the othergaps.

An important advantage that isderived from rotating the arclets aboutthe electrodes 30, 30a as an axis is that the radially-outwardly actingmagnetic loop effect that is present does not oppose the rotary motionof the arclets at any point in their circumferential travel. Thearclets, in moving about the electrodes as an axis, are not required tomove toward the electrodes and, thus, the radially-outwardly acting loopeflect does not interfere with the desired rotary motion. If, on theother hand, the arclets were rotated about some axis remote from theelectrodes, part of the rotary travel would be generally toward theelectrodes, and the radially-outwardly acting magnetic loop circuitwould tend to oppose arc-rotation during this particular portion of therotary travel. Such opposition would tend to diminish the desired highspeed of arc-motion.

The arclets formed. across the secondary arcing gaps 53, 54,, andSS-Will generate metallic vapors that will be ejected radially outwardtoward the insulating casing 11. For protecting the insulating casing 11from being metallically coated by the condensate of these metallicvapors, I have provided a cylindrical vapor-condensing shield for eachsecondary arcing gap. These shields, which are respectively designated73, 75,. and 77, are preferably of metal and are supported on the casing11 by means of the previously-described plates 24 sandwiched between theL-shaped rings 22. The vapors generated by arcing condense on theseshields 73, 75, and 77 before they can reach the insulating cylinders16-21 and thus the cylinders are protected from the build-up of ametallic coating thereon. It is to be noted that each of thesevapor-condensing shields 73, 75, and 77 is electrically isolated fromthe disc-shaped electrode members 4-1-46 oneach side of itscorresponding secondary arcing gap. For example, the shield 73' iselectrically isolated from the disc-shaped electrodes 41 and 42 by theinsulating cylinders 16 and 17; the shield 75 is electrically isolatedfrom the disc-shaped electrodes 43 and 44 by the insulating cylinders 18and 19'; and the shield 77 is isolated from the disc-shaped electrodes45 and 46 by means of the insulating cylinders 20 and 21.

Preferably, the length of the insulating cylinders and the gaps betweenthe disc-shaped electrodes and the shields are so selected that theshield for each secondary arcing gap is at approximately a mid-potentialrelative to the disc-shaped electrodes (41-46) of the correspondingarcing gap when the contacts 3% and 31 are separated. This, incombination with the fact that the opposed electrodes are disc-shapedand of substantially the same configuration, enables the electric fieldin the region of each secondaly arcing gap to be generally symmetricalWith respect to a plane bisecting the arcing gap and extending generallyperpendicular to the longitudinal axis of the interrupter or the contactrods a, 31a. Since substantially all of the vapors liberated by arcingare condensed on the metallic shields before they can reach theinsulating casing, it will be apparent that the midpotentialrelationship of the shield relative to the electrodes of itscorresponding arcing gap is not substantially changed by the metallicparticles. Thus, the generally symmetrical configuration of the electricfield for each arcing gap is retained without substantial change despitethe condensation of metallic vapors on the shield. The generallysymmetrical field relationship is of considerable benefit in minimizingthe polarity effect that has been noted in connection with arcing gapsgenerally. More specifically, it has been noted that arcing gapsgenerally have a lower breakdown strength when subjected to voltage ofone polarity than when subjected to voltage of an opposite polarity. Themore non-symmetrical is the electric field in the region of the gap themore pronounced in this polarity effect. By providing a symmetricalelectric field, I am able to minimize this polarity.

effect. As a result, my interrupter is not subject to the undulyprolonged arcing that could result from low dielectric strength duringalternate half cycles. Because the symmetrical electric field isretained despite vapor condensation on the shields, the beneficialeffects of the symmetrical electric field are retained despite repeatedswitch operations.

To aid in more precisely obtaining the desired voltage distributionbetween the secondary arcing gaps and between the shields and theirassociated electrodes, it is sometimes desirable to connect externalgrading capacitors across, each of the insulators 16-41. Such capacitorscan boot a conventional form and are not shown in the drawing.

Although I prefer to slot the contact disc in the. general mannerillustrated, in. Fig 2, other slot. configurations.

8 are also suitable. however, the disc should be slotted from its outer.periphery inward, and the slot configuration should be such that thecurrent path extending through the disc to an arc:

terminal located at substantially any angular point. on the outerperipheral region has a net component extending generally tangentiallywithrespect to the periphery in the vicinity of the are. In addition,the slot configuration should be such that this net tangential componentextends from the arc in the same angular direction for substantially allangular positions of the are on the peripheral region of the disc, sothat motion of the arc terminal is continued in a single angulardirection. By the term angular direction, used hereinabove, is meant aclockwise of counterclockwise direction relative to the central regionof the disc.

As an example of another slot configuration which meets theserequirements, reference may be had to Fig. 3, which is a plan view of amodified form of the discshaped member. in this arrangement of Fig. 3, asingle slot extends from the outer periphery of the disc 41a inwardlytoward the center of the disc. This slot 80 has an angular extent ofmore than 360 degrees, which is much greater than that of slot 57 ofPig. 2. As a result, this slot 80 is alone sufficient to force allcurrent flowing to an arc terminal located at substantially any angularpoint on the outer peripheral region to follow a path having a netcomponent extending generally tangentially with respect to the peripheryin the vicinity of the arc.

Although I prefer that both of the discs of each gap be slotted, it isto be understood that only a single disc of each gap may be slotted iflower speeds of arc-rotation can be tolerated.

It is to be understood that, in constructing the disclosed vacuuminterrupter, the various parts inside the vacuum. envelope should befreed of the sorbed gases and other contaminants sufiiciently to avoidharmful impairment of the vacuum during operation. Conventional vacuumprocessing techniques can be used for attaining this desired end.

While I have shown and described particular embodiments of my invention,it will be obvious to those skilled in the art that various changes andmodifications may be made without departing from my invention in itsbroader aspects and I, therefore, intend in the appended claims to coverall such changes and modifications as fall within the true spirit andscope of my invention.

What I claim as new an desire to secure by Letters Patent of the UnitedStates is:

1. A vacuum-type circuit interrupter comprising an evacuated envelopedefining a vacuum chamber, a pair of electrodes disposed within saidvacuum chamber and defining therebetween a main arcing gap across whicha circuit-interrupting arc is adapted to be established, a plurality ofpairs of annular disc-shaped members surrounding said arcing gap andradially spaced from said electrodes, the disc-shaped members of eachpair being spaced apart to define between the two disc-shaped members asecondary arcing gap of annular shape surrounding said main gap, meansfor driving said circuit-interrupting are from said main arcing gapradially outward into contact with said disc-shaped members and forthereafter dividing said circuit-interrupting are into a plurality ofseries-related arclets respectively bridging said secondary arcing gaps,means for thereafter driving each of said arclets onto the outerperipheral region of said discshaped members and for providing amagnetic force acting to hold said arclets on said outer peripheralregion for substantially all angular positions of said arclets, meansfor producing motion of said arclets repetitively about the outerperipheral region of said disc-shaped members comprising slot meansextending from. the1outer.

periphery of at least. one. disc-shapedmember: of: each In any of theseslot configurations,

therebetween a main arcing gap across which a pair in such a manner thatthe current path extending through said one disc-shaped member to anarclet terminal located at substantially any angular point on said outerperipheral region has a net component extending generally tangentiallywith respect to said periphery in the vicinity of said arclet terminal.

2. In the vacuum-type circuit interrupter of claim 1, an annulararc-runner surrounding each of said electrodes and extending between itsassociated electrode and one of said disc-shaped members to providemeans for transferring-said main arc'from said main arcing gap to saidsecondary arcing gaps.

3. In the vacuum-type circuit interrupter of claim 1, an annulararc-runner surrounding each of said electrodes and extending between itsassociated electrode and one of said disc-shaped members to providemeans for transferring said main are from said main arcing gap to saidsecondary arcing gaps, means for conducting current to and from saiddisc-shaped members by a path independent of said arc-runners when saidarclets are positioned across said secondary arcing gaps, meansincluding insulation located between said disc-shaped members and theouter periphery of said annular arc-runners for forcing any currentflowing through said runners to an are located on said runners to followa path extending from the inner peripheral region of said annulararcrunners radially outwardly.

4. The vacuum-type circuit interrupter of claim 1 in combination withconductive structure electrically interconnecting the adjacentdisc-shaped members of adjacent arcing gaps and conductive structureelectrically interconnecting the outermost disc-shaped members with theelectrodes of said interrupter, said conductive structure being joinedto said disc-shaped members adjacent their innermost peripheries so thatfor each arcing gap the radially-acting loop circuit defined by thearclet and the current path leading through the disc-shaped member inthe immediate region of the arclet acts in a direction radially outward.

5. An electric circuit comprising a housing,

a pair of electrodes disposed within said housing and definingcircuitinterrupting arc is adapted to be established, a plurality ofpairs of disc-shaped members surrounding said arcing gap and radiallyspaced from said electrodes, the discshaped members of each pair beingspaced apart to define between the two disc-shaped members a secondaryarcing gap of annular shape surrounding said main gap, means for drivingsaid circuit-interrupting are from said main arcing gap radially outwardinto contact with said disc-shaped members and for thereafter dividingsaid circuit-interrupting are into a plurality of series-related arcletsrespectively bridging said secondary arcing gaps, means for thereafterdriving each of said arclets onto the outer peripheral region of saiddisc-shaped members and for providing a magnetic force acting to holdsaid arclets on said outer peripheral region for substantially allangular positions of said arclets, means for producing motion of saidarclets repetitively about the outer peripheral region of saiddisc-shaped members comprising slot means extending from theouter'periphery of at least one disc-shaped member of each pair in sucha manner that the current path extending through said one discshapedmember to an arclet terminal located at substantially any angular pointon said outer peripheral region has a net component extending generallytangentially with respect to said periphery in the vicinity of saidarclet terminal.

6. A vacuum-type circuit interrupter comprising an evacuated envelopedefining a vacuum chamber, a pair of electrodes disposed within saidvacuum chamber and defining therebetween a main arcing gap across whicha circuit interrupting are is adapted to be established, a plurality ofpairs of annular disc-shaped members disposed about said arcing gap andradially spaced from said electrodes, the disc-shaped members of eachpair being spaced apart to define between the two disc-shaped members asecondary arcing gap of annular shape surrounding said main gap, meansfor driving said circuitinterrupting are from said main arcing gapradially outward into contact with said disc-shaped members and forthereafter dividing said circuit-interrupting are into a plurality ofseries-related arclets respectively bridging said secondary arcing gaps,means for thereafter driving each of said arclets onto the outerperipheral region of said disc-shaped members and for providing amagnetic force acting to hold said arclets on said outer peripheralregion for substantially all angular positions of said arclets, meansfor producing motion of said arclets repetitively about the outerperipheral region of said disc-shaped members comprising slot meansextending from the outer periphery of at least one disc member of eachpair in such a manner that the current path extending through said onedisc member to an arclet terminal located at substantially any angularpoint on said outer peripheral region forms with said arclet a loopcircuit having a magnetic efr'ect exerting a net' component of force onthe arclet generally tangential with respect to said periphery, said nettangential force component acting in the same angular direction forsubstantially all angular positions of said arclet on said periphery andthereby causing said arclet to travel rapidly in one angular directionalong the outer peripheral region of said disc member.

7. A vacuum-type circuit interrupter comprising an evacuated envelopedefining a vacuum chamber, a pair of electrodes disposed within saidvacuum chamber and defining therebetween a main arcing gap across whicha ci cuit-interrupting arc is adapted to be established, a plurality ofpairs of annular disc-shaped members disposed about said arcing gap andradially spaced from said electrodes, the disc-shaped members of eachpair being spaced apart to define between the two disc-shaped members ofeach pair a secondary arcing gap of annular shape surrounding said maingap, means for driving said circuit-interrupting are from said mainarcing gapradially outward into contact with said disc-shaped membersand for thereafter dividing said circuit interrupting are into aplurality of series-related arclets respective-1y bridging saidsecondary arcing gaps, means for thereafter driving each of said arcletsonto the outer peripheral region of said disc-shaped members and forproviding a magnetic force acting to hold said arclets on said outerperipheral region for substantially all angular positions of saidarelets, means for producing motion of said arclets repetitively aboutthe outer peripheral region of said discshaped members comprising aplurality of slots formed in at least one of said disc-shaped members,each slot having a mouth located at the outer periphery of said onediscshaped member and each extending from said outer periphery inward,said slots having portions which extend in a generally tangentialdirection with respect to the adjacent periphery of said one disc-shapedmember, the angular direction followed by the generally tangentialportion of each of said slots in departing from the slot mouth being thesame for each of said slots.

8. A vacuum-type circuit interrupter comprising an evacuated envelopedefining a vacuum chamber, a pair of electrodes disposed within saidvacuum chamber and defining therebetween a main arcing gap across whicha circuit-interrupting arc is adapted to be established, a plurality ofpairs of annular disc-shaped members surrounding said arcing gap andradially spaced from said electrodes, the disc-shaped members of eachpair being spaced apart to define between the two disc-shaped members asecondary arcing gap of annular shape surrounding said main gap, meansfor driving said circuit-interrupting are from said main arcing gapradially outward into contact with said disc-shaped members and forthereafter dividing said circuit-interrupting are into a plurality ofseries-related arclets respectively bridging said second ary arcinggaps, means for thereafter driving each of said arclets onto the outerperipheral region of said disc-shaped members and for providing amagnetic force acting to hold said arclets on said outer peripheralregion for substantially all angular positions of said arclets, andarc-rotating means for producing motion of said arclets repetitivelyabout the outer peripheral region of said disc-shaped members, saidarc-rotating means comprising means for generating a magnetic fieldwhich acts on said arclets in a generally tangential direction relativeto said disc members.

9. The interrupter of claim 8 in which said envelope is constructedpartially of insulating material and in which there is provided aplurality of metallic vaporcondensing shields respectively surroundingsaid secondary arcing gaps and disposed between said secondary arcinggaps and insulating portions of said envelope to protect said insulatingport-ions from the condensation of arcliberated vapors thereon, andmeans comprising said protected insulating portions for electricallyisolating the shield of each secondary arcing gap from the disc membersof said secondary arcing gap and for electrically isolating said shieldsfrom each other.

10. The interrupter of claim 9 in which each of said shields is atsubstantially a mid-potential with respect to its associated discmembers while said interrupter is in an open position. 11. Theinterrupter of claim 9 in which each of said shields has a potentialrelative to one of its associatetd disc members in open-circuit positionof the interrupter which is a predetermined percentage of the potentialbetween its associated disc members in open-circuit position of theinterrupter, said predetermined percentage being retained without beingsubstantially changed by the condensation of said metallic vapors onsaid metallic shield even from a time prior to the condensation of saidmetallic vapors thereon.

12. The interrupter of claim 9 in which each of said arcing gaps has anelectric field which is generally symmetrical with respect to a centralplane extending between the disc members of said arcing gap normal tosaid electrodes and which retains its general symmetry despite thecondensation of said metallic vapors on the shield of said arcing gap.

13. In the vacuum-type circuit interrupter of claim 8, an annulararc-runner surrounding each of said electrodes and extending between itsassociated electrode and one of said disc-shaped members to providemeans for transferring said main are from said main arcing gap to saidsecondary arcing gaps.

14. In the vacuum-type circuit interrupter of claim 8, an annulararc-runner surrounding each of said electrodes and extending between itsassociated electrode and one of said disc-shaped members to providemeans for transferring said main are from said main arcing gap to saidsecondary arcing gaps, means for conducting current to and from saiddisc-shaped members by a path independent of said arc-runners when saidarclets are positioned across said secondary arcing gaps, meansincluding insulation located between said disc-shaped members and theouter periphery of said annular arc-runners for forcing any currentflowing to an are located on said runners to follow a path extendingfrom the inner peripheral region of said annular arc-runners radiallyoutwardly.

15. An electric circuit interrupter comprising a housing, a pair ofelectrodes disposed within said housing and defining therebetween a mainarcing gap across which a circuit-interrupting are is adapted to beestablished, a plurality of pairs of annular disc-shaped memberssurrounding said arcing gap and radially spaced from said electrodes,the disc-shaped members of each pair being spaced apart to definebetween the two disc shaped members a secondary arcing gap of annularshape surrounding said main gap, means for driving saidcircuit-interrupting are from said main arcing gap radially outward intocontact with said disc-shaped members and for thereafter dividing saidcircuit-interrupting are into a plurality of series-related arcletsrespectively bridging said secondary arcing gaps, means for thereafterdriving each of said arclets onto the outer peripheral region of saiddisc-shaped members and for providing a magnetic force acting to holdsaid arclets on said outer peripheral region for substantially allangular positions of said arclets, and arc-rotating means for producingmotion of said arclets repetitively about the outer peripheral region ofsaid disc-shaped members, said arc-rotating means comprising means forgenerating a magnetic field which acts on said arclets in a generallytangential direction relative to said disc members.

16. An electric circuit interrupter comprising a housing, a pair ofelectric terminals located at opposite ends of said housing, a pluralityof pairs of annular disc-shaped electrodes located within said housingin generally parallel planes, the disc-shaped annular electrodes of eachpair being spaced apart to define an arcing gap between the electrodesof said pair, means for forcing substantially all current flowingbetween the adjacent annular electrodes of adjacent arcing gaps tofollow a current path adjacent the inner peripheries of said annularelectrodes comprising conductive structure electrically interconnectingsaid adjacent electrodes and located adjacent the inner peripheries ofsaid adjacent annular electrodes, means for conducting current betweenthe outermost annular electrodes and said terminals and forcingsubstantially all of said current to follow a path adjacent the innerpe' riphery of said outermost annular electrodes comprising conductivestructure interconnecting said terminals and said outermost annularelectrodes and located at the inner peripheries of said outermostelectrodes, means for establishing an arc radially inwardly of saidannular electrodes, means for forcing said arc radially outwardly intocontact with said annular electrodes and for thereafter dividing saidare into a series of arclets respectively bridging said arcing gaps, andmeans for rotating said arclets about the outer peripheral region ofsaid disc-shaped members.

17. A circuit interrupter comprising an evacuated envelope defining avacuum chamber, a pair of contacts disposed within said vacuum chamber,one of said contacts being movable with respect to the other of saidcontacts to establish a circuit-interrupting arc therebetween, anannular arc-runner fixed with respect to said envelope and closelysurrounding the movable contact about substantially the entire outerperiphery of said movable contact, means for driving one of theterminals of said circuit-interrupting arc radially outward from saidmovable contact to said annular arc-runner, means for carrying currentto and from any arc terminal located on said annular arc-runnercomprising conducting means located at the inner periphery of saidannular arc-runner, and insulating means for forcing substantially allcurrent flowing through said arc-runner to any arc terminal thereon tofollow a path that extends through said conducting means at the innerperiphery of said annular arc-runner and that forms with an are at anypoint on said annular arcrunner a radially-outwardly-acting magneticloop circuit.

18. In an electric circuit interrupter comprising a housing, a pair ofcontacts disposed within said housing, one of said contacts beingmovable relative to the other of said contacts to establish acircuit-interrupting are therebetween, an annular arc-runner fixed withrespect to said housing and closely surrounding the movable contactabout substantially the entire outer periphery of said movable contact,means for driving one of the terminals of said circuit-interrupting arcradially outward from said annular arc-runner aradially-outwardly-acting magnetic movable contact to said annulararc-runner, means for loop circuit. carrying current to and from any areterminal located on said annular arc-runner comprising conducting means10- Refel'finces Cited in the file of this Patent cated at the innerperiphery of said annular arc-runner, 5 UNITED STATES PATENTS andinsulating means for forcing substantially all current 2 027 836 Rankinet a1 Jan 14 1936 flowing through said arc-runner to any are terminal2:051:378 Hampton et 1936 thereon to follow a path that extends throughsaid conducting means at the inner periphery of said annular arc-FOREIGN PATENTS runner and that forms with an are at any point on said10 389,463 Great Britain Mar. 6, 1933

